This invention relates to an automatic transmission for vehicle and more particularly to a fluid pressure control system for governing a planetary or epicyclic gear trains employed in the transmission.
As used herein, the term "low position" refers to a high ratio differential achieved by the planetary gear trains adapted for the slowest travelling speed of the vehicle.
The term "second position" refers to a middle level ratio differential achieved by the gear trains adapted for the middle level vehicle travelling speed.
The term "top position" refers to a position in which the entire mechanism of the gear trains is locked together as a unit and is rotated in integral with an input shaft for achieving a higher travelling speed of the vehicle.
In known automatic transmission, there is usually a time lag in restoring the gear trains to the original mode of operation of low ratio differential after sudden or urgent acceleration, so-called "kick down", of the vehicle is completed by a high ratio differential.